Piston-cylinder assembly of plastic material as well as process and apparatus for its manufacture

ABSTRACT

A clutch master assembly made of plastic material for an automotive vehicle. The assembly a plastic cylinder housing (1) and a piston (2) and a plastic bushing (3). The plastic bushing is arranged to allow it to be screwed in by means of a thread portion (4) which is located in the housing. By the screwing-in of the bushing a grooved disc (5) and a grooved cup (6) are secured in the assembly. The grooved cup is furnished with knobs (21, 22, 23) which exert a force in axial direction on the arrangement consisting of the grooved cup (6) and the grooved disc (5). The piston-side enlarged end of the piston rod (31, 104) is secured within the piston (2, 103) by a back injection.

This is a division of co-pending U.S. application Ser. No. 07/455,363filed on Jan. 9, 1990 now U.S. Pat. No. 5,121,686.

BACKGROUND OF THE INVENTION

This invention relates to a piston-cylinder assembly of plasticmaterial, of glass fiber reinforced plastic, for a master assembly forhydraulic systems in automotive vehicles, and to a process and anapparatus for its manufacture.

In the published German patent application No. 3149628.8, aball-and-socket joint connection is described between a push rodfurnished with a ball head and a pressure element, between the push rodand a piston of a hydraulic brake power booster or master cylinder. Thepush rod is swingably inserted in a base bore of the piston and aretaining element which simultaneously serves as a reinforcing elementand partly surrounds the ball head being arranged between the base boreand the ball head. It is proposed in the patent application that theretaining element is provided with a plurality of elastic projectionssome of which are formed with offsets which back-grip the ball, whereasthe others abut with an initial stress against the wall of the basebore.

In International Patent Application No. WO 87/03344 (PCT application) acylinder is disclosed which is applied in a hydraulic system. Thecylinder is composed of two parts. Each part is made of plasticmaterial. One part comprises an external shell which presents anopening. An end wall is provided at the opposite end. The other partcomprises an internal bushing. The bushing is precision-fitted withinthe shell. It extends from the forementioned open end to thefore-mentioned end wall. The end of the forementioned bushing which isdisposed distant from the open end is located at a distance from the endwall. A cylindrical bore is provided in the bushing. A piston isslidingly arranged within the bore. The piston can move in the directionof the end wall and away from the end wall.

Sealing means are provided which abut against the circumference of thepiston. The sealing means are retained between the internal end of thebushing and the opposite surface of the shell. A pressure chamber isarranged between the end wall and the piston.

Furthermore, a hydraulic master cylinder is described in the Britishpatent application No. GB 2071797A which comprises a cylinder and asupply tank manufactured separately. The supply tank is fastened on thecylinder. The supply tank and the cylinder are interconnected in such amanner that hydraulic fluid may flow between the supply tank and thecylinder during operation. The supply tank has projecting arms which arein abutment against the outside cylinder wall, against opposite sides ofthe cylinder. These arms serve to keep the supply tank and the cylindertogether, so that they can be put into operation jointly. The supplytank is made of plastic material.

Known piston-cylinder assemblies have a complicated set-up which isunsuitable for mass production. In many cases, metal supporting orreinforcing elements are required, since the plastic bodies alone arenot capable of absorbing the mechanical forces. In addition, the knownassemblies require expensive mechanical machining.

Accordingly, the invention has the following objects. In piston-cylinderassemblies, particularly in clutch master assemblies, the sealing cupwhich serves to seal the piston within the cylinder frequently is passedover uncontrollably In many cases, the reason is that the cup has anaxial play. It is one of the objects of the invention to achieve apositioning of the cup without such play. It has been proposed toprovide springs and sheet metal elements to exert an axial pressure onthe cup and, thus, to contribute to the positioning of the cup. Thecombination of plastic material elements and sheet metal elements isunfavorable because this leads to malfunctioning and reduces the servicelife of the piston-cylinder assembly. In addition, such a combination isexpensive, in particular for mass production, and does not allowautomation with regard to the manufacture and to mounting. Therefore, itis another object of the present invention to render such sheet metalelements and springs superfluous. Furthermore, the other metalcomponents, such as retaining metal sheets, cup elements, etc. which areto reinforce and support, which are utilized in the known assemblies areavoided.

It is, moreover, an object of the present invention to use phenolicresin as a material.

In addition, less components than in known devices are utilized for theset-up of the piston-cylinder assembly. The costs of manufacture thereofare reduced. Further, the invention should provide the possibility ofconnecting the cylinder of the assembly, if it is mounted in thepassenger compartment, to the hydraulic system from the enginecompartment.

Glass fiber reinforced plastic is machined only with difficulty. It isnot weldable. These inconveniences which are due to the material areavoided by the present invention. In particular, the invention safelyabsorbs the forces caused by the high pressure in the cylinder through aplastic material thread. Manufacture and mounting of the entirepiston-cylinder assembly are easily accomplished. In particular,favorable conditions are created for a mechanical and automated massproduction.

The cutting or machining operations which were necessary in knownpiston-cylinder assemblies are reduced considerably by the presentinvention. The breather bore of known master cylinder assemblies areavoided. In the known devices, the breather bore represents aproblematic detail which leads to heavy wear of the cups in thepiston-cylinder assembly. The known master cylinders comprise numerouscomponents which require in many cases machining in a highly expensivemanner. The present invention has the further object to considerablyreduce the number of components required.

The manufacture of the master cylinder should involve lower costs thanknown devices. The inventive master cylinder provides a design whichoffers ease of mounting and is, in particular, suitable for a low-costmass production. The present invention provides conditions for amechanical final mounting of the assembly in its entirety.

Duroplast material is applied at an increasing extent as a material forthe manufacture of plastic cylinders. In many cases, duroplast isreinforced with glass fibers Mechanical machining of duroplast, inparticular if it is reinforced with glass fibers, is expensive anddifficult. The service lives of the tools are in part unreasonablyshort. Consequently, it is another object of the present invention toprovide processes and apparatus for the realization of the processeswhich either avoid any mechanical machining or reduce machining to asignificant extent.

In accordance with the present invention, these prerequisites arefulfilled in that the plastic components of the master assembly do notrequire any supporting or reinforcing metal elements as is the case ofknown plastic cylinders. Among others, it is an object of the inventionto utilize the duroplast piston material by itself, that is, withoutmetal auxiliary means for securing the ball-shaped head of the pistonrod in the piston. This means that no clips and springs are necessary asis the case in known devices to connect the piston rod to the piston. Inthis regard, such metal elements cannot be used in combination withduroplast as duroplast is to brittle.

Strict observance of the dimensions of the inside contours of thehousings of cylinders which are made of plastic material is problematicin the known devices. This applies, in particular, if and when thehousings are manufactured by plastic injection molding processes in massproduction. It is an object of the present invention to achieve a higherdimensional accuracy of the inside contours of the housings. It is afurther object of the present invention to improve and to reduce thecost of mass production of plastic cylinders, in particular of plasticmaster cylinders for the automotive vehicle technology, whilesimultaneously maintaining an elevated dimensional accuracy of theinside contours. Moreover, conditions are provided by the presentinvention which render it possible to manufacture the entire cylinderhousing in mass production in its final shape with dimensionallyaccurate inside contours substantially by plastic injection moldingalone. Any cutting or machining is, for example, avoided.

It is another object of the present invention that bosses, burrs, inparticular mold division burrs which come about when two-part tools areused do not introduce problems in the event of subsequent assembly ofthe cylinder or impair the functions of the cylinder. As an alternative,the present invention provides that in the course of the manufacturingprocess such bosses, burrs, etc. are eliminated, and, particularly,sheared off.

SUMMARY OF THE INVENTION

According to the invention, these and other objects are achieved in thata hollow cylinder (bushing) made of plastic material is provided as aguide for the plastic piston which is arranged in the plastic cylinderhousing to allow its being screwed in by means of a thread originated inthe course of the manufacturing procedure of the housing and which inthe mounted condition exerts an axial pressure on a coaxially disposeddisc and a coaxially disposed cup. A particularly compact and, thus,space-saving design results in that the disc is furnished with radiallydisposed hydraulic fluid ducts, in particular in the shape of grooves(grooved disc). For this purpose, in the range of the disc the hollowcylinder and the housing of the assembly form an annular duct whichconnects the radial ducts of the disc to the hydraulic fluid influx ductconnected to the hydraulic fluid supply tank.

In a preferred embodiment, in the range of its end projecting into thepressure chamber, the piston is formed with a projection which in itspreferably slightly conically shaped generated surface presents at leastone longitudinal groove which establishes a hydraulic connection betweenthe radial ducts and the pressure connection between the radial ductsand the pressure chamber in the retracted position of the piston. In asimplified but favorable embodiment the cup is arranged as a valvepermitting the intake of hydraulic fluid through the longitudinalgrooves when the piston is being retracted and establishing a hydraulicseal between the piston and the housing when the piston is advancing.

The disadvantageous prior-art springs and metal elements advantageouslyare avoided by the present invention in that the cup is provided withaxially arranged knobs which serve as elastic elements and which keepthe cup-and-disc arrangement under axial pressure when the hollowcylinder is screwed into the housing. It is, furthermore, provided thatthe cup is furnished with a sealing lip which exercises the valvefunction. Still further any particular means of reinforcement to form astop for the piston are unnecessary because at its pedal-side end, thehollow cylinder can be provided with a molded, particularly radiallyinwardly extending stop for the piston.

For the purpose of simplification and cost reduction for the manufactureof the piston-cylinder assembly, the hollow cylinder can be arranged soas to be screwable into the housing of the assembly by means of a threadwhich is provided during the manufacturing process by the spindling-outof a tool.

In those cases in which the master cylinder is mounted in the passengercompartment a pressure nozzle may be arranged as a piece of pipe whichconnects the assembly with the hydraulic fluid line leading to the othercomponents of the hydraulic system. This arrangement may then beprovided in an opening in the splash shield of the engine compartmentand furnished with a flange-type screw fitting such that the cylinder ofthe assembly is connectible from the engine compartment. Anotheradvantageous embodiment of the present invention is distinguished by thefact that the piston-side, radially enlarged end of the piston rod issecured within the plastic material piston by a back injection,preferably by a back taper or back gripping.

As a significant improvement over known devices, in its range disposeddistant from the pressure chamber, the primary groove for the primarycup is furnished with an annular duct arranged in the cylinder housing,preferably with a recess, and preferably through a duct located in thecylinder, the annular duct is in hydraulic connection with the supplytank for the hydraulic fluid.

A particularly low-cost mounting of the piston-cylinder assembly isachieved in that the hydraulic fluid outlet which represents thehydraulic link between the pressure chamber of the assembly and theother components of the hydraulic system is formed by a pipe which isflared in the range of its pressure chamberside end as is provided, inthe range of its exit from the cylinder in radial direction, with atleast one pinching in radial direction leading to at least one pinchingin radial direction leading to at least one bulging in the unpinchedrange of the circumference of pipe. The pinching is made in the event ofmounting of the pipe within the cylinder, wherein the flaring togetherwith the bulging provide means for fixing the pipe within the cylinder.

Another low-cost manufacture is attained by the present inventionwherein the cutting or machining operations are reduced to aconsiderable extent. The conventional breather bore is eliminated. Themaster cylinder in accordance with the present invention provides easeof mounting, as the housing and the piston each comprise but one part atthe moment of final mounting. Supporting sheet metal elements areavoided. Therefore, the present invention provides that duroplastbecomes applicable to master cylinders. Duroplast is a plastic materialthat withstands the elevated temperatures in the engine compartmentwhere the master cylinder is accommodated. No clips and spring asaccording to long-accepted teachings of the prior art are required toretain the ball-shaped head of the piston rod of the present invention.

With regard to the process taught by the present invention, the objectsproposed are, moreover, achieved in that upon the injection procedure, afirst tool is spindled out of the cylinder housing by means of a threadand subsequently a second tool is extracted from the cylinder housing.For the application of the process for the manufacture of a housingwhich comprising a cylindrical chamber having a plurality of diameters,in particular of a stepped cylindrical chamber, it is taught herein thatthe first tool is spindled out of the range of the chamber having thelarger diameter, that subsequently the second tool is extracted from therange of the chamber having the smaller diameter. A further improvementof the process according to the present invention consists in thatbosses, burrs, etc. which are due to the manufacture, in particular molddivision burrs, are sheared off in the event of extraction of the secondtool. For the purpose of carrying out the process, an apparatus isprovided which is distinguished in that a first tool furnished with athread is provided which is arranged so as to allow spindling out of thecylinder housing, wherein a second tool is provided which is arranged toallow extraction from the cylinder housing.

For the realization of a process for the manufacture of a housingcomprising a cylindrical chamber having a plurality of diameters, inparticular of a stepped cylindrical chamber, a first tool is furnishedwith a thread which presents a diameter corresponding to the largerdiameter of the cylinder and which is arranged to allow spindling out ofthe cylinder. A second tool is provided which presents a diametercorresponding to the smaller diameter of the cylinder and which isarranged to be extractable from the cylinder. As a further feature ofthe present invention, the first tool is provided in the shape of abushing, the second tool is arranged in the shape of a piston which isarranged within the bushing at least partly during the manufacturingprocess.

According to still other features of the invention, a housing for acylinder is provided which is manufactured by the described processesand/or apparatus and in which it is provided that the wall of thecylinder surrounded by the housing is furnished with a thread fabricatedby spindling-out the tool. The thread serves as a fixing means, inparticular as a means for screwing in further components of the cylinderin the course of the assembly thereof. Finally, an injection moldingprocess is provided for the manufacture of the piston-cylinder assemblyaccording to which the piston rod and a core surrounding the piston rodare arranged. The assembly is arranged in a first process step, in aninjection die mold corresponding to the external shape of the piston, ina second process step the unit comprised of the piston rod and the coreis embedded by injection of plastic material, and in a third processstep the core is removed. In a further embodiment of the process inaccordance with the present invention, that piston-side end of thepiston rod which is enlarged in radial direction is embedded by injectedplastic material in such a manner that under formation of a back taperor back gripping a certain force of extraction is transmitted to thepiston by the piston rod.

BRIEF DESCRIPTION OF THE DRAWING

These and other details of the present invention will be described ingreater detail in the following description of two embodiments of theinvention taken in conjunction with the accompanying drawing, in which:

FIG. 1 shows a cross section of the piston-cylinder assembly in axialdirection;

FIG. 2 shows a cross section of a grooved disc in axial direction;

FIG. 3 shows a view of the grooved disc according to FIG. 2 in thedirection of the arrow III in FIG. 2;

FIG. 4 shows the profile of a grooved cup;

FIG. 5 is a cross sectional representation of another design of thepiston-cylinder assembly, the cross section running through the axis ofthe assembly;

FIG. 6 is a cross sectional representation along the sectional lineII--II in FIG. 5;

FIG. 7 is a cross sectional representation along the sectional lineIII--III in FIG. 5; and,

FIG. 8 is a diagrammatic representation of the apparatus to carry outthe process according to the invention.

DETAILED DESCRIPTION

In FIG. 1, a piston-cylinder assembly of plastic material is shown whichprovides a master assembly for a hydraulic clutch actuating system in anautomotive vehicle. Reference numeral 1 denotes the plastic housing. Thepiston bears the reference numeral 2. The bushing 3 is screwed into thehousing 1 by means of a threaded portion or thread 4. The threadoriginates from and is provided during the manufacturing process(plastic injection molding process). The bushing guides the piston andretains the grooved disc 5 and the grooved cup 6 in their positionsshown in FIG. 1. Reference numeral 7 denotes a further sealing cup. Thescrewed-in bushing safely secures the arrangement comprising the groovedcup and of the grooved disc. Details of the grooved disc are bestillustrated in FIGS. 2 and 3. These Figures reveal the radially arrangedducts 8, 9, 10, 11, 12, 13, 14, 15 or grooves. The radially arrangedgroove 13 additionally is shown in FIG. 1.

The piston 2 is furnished with a pressure chamberside projection 16provided with longitudinal grooves 17, 18. At the left end of thehousing 1 as shown in FIG. 1, a pressure nozzle 19 is located whichconnects the pressure chamber 20 with a hydraulic fluid line. Thehydraulic fluid line leads to the slave cylinder of the hydraulicclutch.

The particular profile of the grooved cup 6 is illustrated in FIG. 4. InFIG. 4, reference numerals 21, 22, 23 denote knobs which extend in axialdirection and which are in abutment against the lateral wall 24 of thestep 25 as is illustrated in FIG. 1. The knobs function as springelements which keep the arrangement of the grooved cup and of thegrooved disc tensioned when the bushing is in the screwed-in position.Due to the foregoing and due to the screwed-in bushing 3, a positioningwithout play of the grooved cup and the grooved disc is provided.Reference numeral 26 in FIG. 4 denotes a sealing lip which provides avalve function as will be explained more fully hereinafter. The sealinglip 26 is arranged juxtaposed to the generated surface of the piston,while the knobs are positioned in the range of the radially outsidesurface of the step 25.

In the situation illustrated in FIG. 1, hydraulic fluid may flow fromthe hydraulic fluid supply tank (not shown) through the duct 27 into theannular chamber or annular duct 28. This annular duct is formed by thebushing 3, the cylinder housing 1 and the grooved disc 5. The hydraulicfluid contained in the annular duct may reach the longitudinal grooves17, 18 through the radial ducts 8 to 15. From the longitudinal grooves17, 18, the hydraulic fluid flows into the pressure chamber 20. In thatsituation as illustrated in FIG. 1, the piston is retracted to theright, and due to the pressure exerted by the spring 29 it is inabutment against the stop 30 being molded at the bushing 3. Uponactuation of the clutch pedal, the piston 2 is moved to the left due tothe action of the push rod 31 which is swingably embedded by injectionwithin the phenolic resin piston 2 and which presents a ball 32 suitablycoated with grease. The edge 33 of the piston passes over the sealinglip 26. As a consequence, the connections between the radial ducts 8 to15, on one hand, and the pressure chamber 20, on the other hand, areinterrupted. Pressure will build up within the pressure chamber 20. Thesealing lip 26 comes into abutment against the external generatedsurface of the piston. The grooved cup with its sealing lip now assumesthe closing function as a valve.

In FIG. 5, a plastic clutch master cylinder 101 of an automotive vehicleis illustrated which is furnished with a plastic housing 102. Within thehousing, the piston 103 made of plastic is guided to be moved by aclutch pedal (not shown). The force of the clutch pedal is transmittedto piston 103 through the piston rod 104. At its lefthand end piston rod104 presents a ball-shaped head 105 which is embedded in plastic byinjection so that a force of extraction in the direction of the arrow106 is transmitted to the piston 103 by the piston rod 104. Referencenumeral 107 denotes the pressure chamber. The hydraulic fluid outlet isshown generally at reference numeral 108.

The manufacture of the clutch assembly according to FIG. 5 takes placein a plurality of steps. The piston rod and a core are accommodated inan injection die mold corresponding to the external shape of the piston.The core occupies the range of the annular chamber 109 arranged tosurround the lefthand part of the piston rod. The piston rod and thecore are embedded in plastic by injection. Subsequently the core isremoved A back injection, respectively a back taper or back gripping ofthe ball head 105 is obtained in this manner in the range 110. Backtaper represents a safe connection between the piston rod and thepiston. This connection is made sufficiently sturdy as to permit thetransmission of a force of extraction of, for example, 100 kg. It willbe appreciated by those skilled in the art that the master assembly inaccordance with the present invention does not require any additionalsecuring and supporting metal elements such as are utilized in prior artfor fixing of the piston rod within the plastic piston.

Reference numeral 111 denotes a recess in the housing 102. Recess 111 isdisposed in a range of the bottom of the primary groove 112 for theprimary cup 127 which is disposed distant from the pressure chamber 107The recess 111 assumes the function of the conventional breather bore.In the pressureless condition the hydraulic fluid flows through the duct113 (see also FIG. 6) which establishes the connection to the hydraulicfluid supply tank (not shown), through the recess 111 and through theclearances 114 arranged radially outside at the lefthand end of thepiston 103 forth into the chamber 109. When the clutch pedal isactuated, the piston 103 will be translated to the left by the pistonrod 104. The edge 115 will pass over and close the recess 111 When thepiston 103 is moved further to the left, the edge 115 will pass over thesealing lip 116 of the primary cup 127. The sealing lip 116 willsealingly be pressed against the generated surface of the piston 103 bythe pressure building up in the pressure chamber 107. Hydraulic fluidwill be conveyed through the outlet 108 to the slave cylinder of thehydraulic clutch actuating system. The position and the configuration ofrecess 111 as well as its connection to the duct 113 are bestillustrated in FIG. 6.

The hydraulic fluid outlet 108, see FIGS. 5 and 7, is formed by a pipewhich is accommodated in the wall 117 of the cylinder 102. The pipe isprovided with a flared end 118. Relative to the wall, two pinchings aremade which are opposed to the flared end 118. The position of thepinching 119, 120 is illustrated in FIG. 7 These pinchings causebulgings 121, 122 which radially surmount the diameter 123 of theopening 124 in the wall 117. The bulgings 121, 122 jointly with theflared pipe end 118 fix the pipe 125 in the wall 117 of the cylinder.The original generatrix of the pipe, that is, the generatrix existingbefore the pinching operation and which at that time is perfectlycircular is shown by a dashed line in FIG. 7 and bears reference numeral129. For the purpose of mounting of the pipe 125, the pipe is insertedwith its flaring 118 into the opening 124 from the inside Subsequently,the pinching is made on the outside.

Reference numeral 126 denotes a Seeger circlip securing the pistonwithin the cylinder housing. The flange 128 is connected to the pedalblock The position of the splash shield of the vehicle may be to theleft of the flange, see FIG. 5, as the automotive vehicle manufacturermay require. This is of advantage, as the automotive vehiclemanufacturer is free to position the splash shield as desired.

Finally, in FIG. 8 a first tool bears reference numeral 211 and a secondtool reference numeral 212. The first tool has a bushing-shapedconfiguration and is furnished with a thread 213 on its surface.

The second tool 212 has a piston-shaped configuration and is arrangedpartly within the bushing-shaped tool 211 in FIG. 8. For clarity, thefirst tool 211 is illustrated in FIG. 8 hatched from top left to bottomright, in an axial cross section. In its axial sectional view, thesecond tool 212 is illustrated with a hatching from bottom left to topright. The axis of the two tools is marked by the dash-dotted line 214.

Manufacture of the cylinder housing takes place in the following processsteps. First of all, plastic is injected in the mold for the housing,during which procedure the first and the second tool are embedded inplastic. Subsequently, the first tool is spindled out, that means, thefirst tool 211 is screwed out of the range 216 of the housing 1 by thethread 213. In the next process step the piston-shaped second tool 212is extracted from the housing 1 to the right, in the direction of thearrow 220. A mold division burr may form in the range of the surface ofthe inside wall of the housing, which is sheared off in the course ofextraction of the second tool 212. After the first tool 211 has beenspindled out, the housing 1 presents a thread 213 This thread may beutilized to screw in, for example, the component 3 (FIG. 1) to assemblethe master cylinder.

As is illustrated in FIG. 8, the processes and apparatus according tothe present invention allow manufacture of cylinder housings which havea stepped configuration. In FIG. 8, six diameters 217, 215, 223, 218,222, 219 are illustrated in this regard.

What is claimed is:
 1. A process for manufacturing a cylinder housing ofa piston cylinder device comprising the steps of assembling a first toolcomprised of an externally threaded bushing over one end of an elongatesstepped diameter second tool, said second tool being formed with aplurality of shoulders of progressively increasing diameter towards saidone end thereof to form a stepped configuration, said one end thereofbeing of reduced diameter and said external thread of said first toolbeing of larger diameter than the largest diameter of said secondtool;molding plastic around said assembled first and second tools so asto form a cylinder with said first and second tools embedded therein;rotating said first tool to be unthreaded from a portion of saidcylinder formed thereover with an internal thread; and thereafteraxially withdrawing said stepped diameter second tool from said moldedcylinder, whereby a cylinder housing having a stepped diameter with aninternal thread formed at one end is produced.
 2. A cylinder housing ofa piston cylinder device as manufactured by the process of claim 1.